This was just normal card stock. Nothing fancy. The 90lb was a little thin for some parts, so I re-enforced it by glueing another layer to the back. This was only a problem with some large, flat areas, and not for most of the mech. I think the next paper weight up was 110lbs. I might try that, but no heavier.
I think the sheet count was somewhere around 25. The sheets are all lettered from A to U, but some of them must be printed twice for symetrical parts.
Good luck.